For series resonant (or variable frequency resonant) circuits, the Q factor increases with the increase of inductance. Therefore, when calculating elements, the quality factor should be taken into account. 

The resonance phenomenon allows the use of series resonant circuits as frequency dependent circuits and filter elements. 

General Information

A series resonant circuit is a circuit composed of capacitors and inductors, used to generate free cable oscillations in radio receivers and transmitters. This device is used as various filters (bandpass and notch). This radio component is used to adjust the signal in the direction of increasing or decreasing amplitude. The main function of this circuit is frequency filtering.

This device is widely used in the military field. Noise suppression filters are used for radar. The enemy uses various jammers to prevent target detection. The device includes a special device composed of ordinary circuits, but its core is made of a special alloy. Interference is' filtered out ', allowing radar operators to have a complete understanding of the air situation.  

This device can also be used for automation. For example, an aircraft includes a frequency control unit. Its main components are two circuits that are tuned to only two frequencies -760 and 840 Hz. They receive voltage at a frequency of 790 Hz from a special generator. The latter only emits 395 Hz. If the frequency deviates downwards from the nominal value, the reactance of one of the circuits will decrease.

Afterwards, activate the electronic device of the unit and send a signal to increase the speed of the generator. When the frequency exceeds the rated value, the reactance of the other circuit increases. As a result, automation was triggered and another signal was received to reduce the speed of the generator.